Buffer Components
Buffer Components
Definition
An SAP buffer consists of the following parts:
Mode table |
The mode table resides in shared memory and tells you which pool contains which shared memory areas. The mode table is part of the common information on the shared memory areas that are accessed by the work processes. For example, SAP Key 1 with Mode = 0, instructs the OS kernel to extract this buffer from the default pool and to allocate a unique shared memory segment. SAP Key 10 with Mode = pool size instructs the OS kernel to store the buffer specifically in pool 10. SAP Key 11 with Mode = -10 means that the buffer is located in pool 10. |
SAP Global Management Table |
A shared memory area that is allocated by the dispatcher during system startup. When semaphore protection is on, the SAP Global Management Table is addressed exclusively by SAP Shared Memory Management. This is a central agent that is found in each work process and that sets up a shared memory area for the local application server or instance. The SAP Shared Memory Management issues a call to the operating system (OS) when it creates a shared memory area. As a result, the SAP key is assigned to an OS key. The OS returns a unique identifier (handle) for the shared memory area, with which the SAP Shared Memory Management addresses the shared memory area that was created by the OS. All work processes in the SAP System can access the SAP Global Management Table. The handle can be accessed by all work processes. |
Address Table |
Every work process contains this table. Assigns virtual addresses to the physical addresses of the shared memory areas. |
Shared Memory Objects |
These include the buffers, for example. |
Header |
Contains information on the shared memory area (also called memory segment). If a write error occurs outside the segment area, then the uniformity of the header is destroyed. The control function of the SAP Management of Shared Memory checks the consistency of the headers. |
ID |
Identifies the memory area. The ID is assigned when a SAP Shared Memory Management user requests the memory area. |
Storage Class |
The memory class. Examples of memory classes: permanent (local), shared, roll, paging and short. |
Subdivision |
A mark for the requested area that can be referred to later when you release the memory area. |
Size include header |
Buffer size including the header. |
Alignment |
Alignment of memory areas in accordance with hardware constraints. |
See also:
Buffer Synchronization Buffer Types